(a) Field of the Invention
The present invention concerns a semiconductor device which exhibits a very steeply rising current versus voltage characteristics and which has a very small output resistance. These characteristics are provided by the feedback action of the gate current flowing through a resistance distributed between the gate region and a primary current channel region.
(b) Description of the prior art
In a field effect transistor (hereinafter to be referred to as FET), when the drain voltage is small as compared with the saturating drain voltage, the drain current increases linearly with the drain voltage. That is, the drain current vs. drain voltage (V.sub.d /I.sub.d) relationship is similar to a resistance. This relationship between the current and the voltage is not dependent upon the particular structure or type of the FET, and is manifested in both junction FET's (hereinaffter referred to as JFET) and insulated-gate type FET's (hereinafter to be referred to as MOS-FET).
A static induction transistor (hereinafter to be referred to as SIT) exhibits a non-saturating current versus voltage characteristic. Under gate bias conditions that provide carriers within the channel region, the SIT also exhibits a substantially linear current versus voltage characteristics. Needless to say, there the current tends to saturate at high levels of drain voltage.
Under bias conditions whereby the channel region of an SIT is completely pinched off, a potential barrier is produced in the foreground of the source region. This potential barrier decreases in response to an increase in the drain voltage. Thus the number of carriers flowing from the source toward the drain will increase in substantially exponential relation to the drain voltage. Thus, for small drain currents, the drain current I.sub.d increases exponentially relative to the drain voltage V.sub.d. Expressed mathematically, (particularly for reverse gate bias operation): ##EQU1## wherein: .eta. represents structural parameter (numerical)
.upsilon. represents voltage amplification factor; PA0 q represents unit electric charge; PA0 k represents Boltzmann constant; and PA0 T represents absolute temperature.
In other words, the increase in drain current can be expressed basically in terms of Maxwell-Boltzmann statistics.